Astronomers have discovered a new pink dwarf planet that has the most distant orbit in our solar system.
The discovery suggests there could be thousands of similar planets beyond the known edge of our solar system but within the influence of our sun.
The new dwarf planet, officially named 2012 VP113, is about 450 kilometres in diameter — a little bit less than the length of Lake Michigan.
It never comes closer to the sun than 12 billion kilometres or 80 astronomical units (AU) — that is, 80 times the distance between the sun and the Earth, according to a study published online Wednesday in the journal Nature.
The previous furthest object from the sun was the dwarf planet Sedna, which was found at 78 AU about a decade ago, and named after the mythological Inuit goddess who created the sea creatures of the Arctic.
At that time, astronomers weren't sure whether Sedna was an oddity, a lone resident of a region known as the inner Oort cloud, beyond the Kuiper belt where the dwarf planets Pluto and Eris reside.
After the discovery of VP113, "we're pretty confident now that Sedna's not unique," said Chad Trujillo, an astronomer at the Gemini Observatory in Hawaii and the lead author of the study, in a podcast interview with Nature.
He now thinks there may be many similar objects in the inner Oort cloud, although they rarely come close enough to see with a telescope.
"There could be hundreds of thousands if not more. We don't really know."
VP113 has no common name, unlike Sedna and Pluto, but it has been nicknamed "Biden" after the U.S. vice-president Joe Biden because of its initials, according to a news release from the Carnegie Institution.
VP113 was discovered using the new Dark Energy Camera on the NOAO 4 meter telescope in Chile by Trujillo and Scott Sheppard of the Carnegie Institution for Science in Washington, D.C. The researchers took photos of the sky about every two hours and looked for objects moving relative to a motionless background of stars.
The new planet appears pink — far less red and shiny than Sedna. Trujillo said researchers don't know what it's made of, but because of its distance from the sun "it must have a lot of ice on its surface."
VP113 and Sedna have similar, elongated orbits suggesting they may be influenced by a huge planet up to 10 times the size of the Earth deep in the Oort cloud. While Sedna can approach closer to the sun than VP113, the dwarf planet's elongated orbits mean there are times when VP113 is closer to the sun than Sedna.
Trujillo said scientists don't know how objects like Sedna and VP113 formed, but the prevailing theory is that they were dragged away from the inner solar system by a star passing close by the sun shortly after the sun was born.
He added, "The really interesting thing about Sedna and VP113 is it sort of shows how little we know about our own solar system."
In this orbit diagram for the outer solar system, the sun and inner planets are at the center. The orbits of the four giant planet Jupiter, Saturn, Uranus and Neptune are shown by purple solid circles. The Kuiper Belt (including Pluto) is shown by the dotted light blue region just beyond the giant planets. Sedna's orbit is shown in orange while 2012 VP113's orbit is shown in red. (Scott S. Sheppard/Carnegie Institution for Science)
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